Weights vs. Cardio: Keep Them Separate or Combine?

Not sure if you should hit the elliptical or jump straight on to the weight bench? Confused about whether or not you should lift on the same day as a run? You're not alone. Let's take a deep dive into the research and determine what to do and when.

A few days ago I received a message on Facebook from listener Lindsey. She said:

“In a recent episode you talked about how aerobic exercise and weight lifting affect each other, but I'm not sure I understood. As a runner, can I run to the gym to lift weights and run home again or should I keep the cardio and weights on separate days? Thanks for your help!”

After thanking Lindsey for her great question, I promised that I would do a deeper dive in the near future. I also told her that, in a nutshell, if she wants to get the fullest benefits of each workout, she should separate them. But since she is primarily a runner (and probably not too concerned about packing on as much muscle as possible), doing a short run to warm-up for and cool-down from a strength session is a great way to maximize her time and put a few more miles on her legs but not to do that every day. To be a good runner, she must also have dedicated run days.

Now, if I were Lindsey, I would have written back and asked me a follow-up question that would have gone something like this: “If I do want to get the fullest benefits of each workout, how much would I have to separate those workouts by?”

Well, good question, imaginary Lindsey. Let’s look at that!

How Long Should You Wait Between Workouts?

Avoid scheduling two contradictory workouts, with less than a six-hour recovery period between them.

So, like I told Lindsey, if your goal is to get strong, there is some significant detriment that cardio can have on strength development. This is true whether you do the cardio workout in the same workout, or if you simply do cardio less than six hours before your weight training.

The researchers who performed this study also stated that daily training without a recovery period between sessions (or training twice a day) is not optimal for neuromuscular and aerobic improvements. So ideally, if you want to get stronger, you should separate your cardio and strength workouts by more than six hours.

Now, this seems straightforward for someone like Lindsey who is mostly interested in running and is doing strength training because she is a smart runner who understands the value of pre-hab. But what if the event you are training for requires that you perform strength and cardio simultaneously? Like an obstacle course race, the CrossFit Games, or even a killer hike with a big pack on your back? Or perhaps your goal is simply to lose body fat. Well, that changes everything.

Combining Weights and Cardio

A study that aimed to investigate the effects of intrasession sequencing (the order) of concurrent resistance and endurance training on the serum leptin (the hormone that inhibits hunger), testosterone, cortisol (the stress hormone), and body composition in obese men, came to some cool conclusions.

The “weights before cardio” group were slightly better off in every single test, including fat loss.

Thirty obese young males were divided randomly into three groups that either performed weights before cardio, cardio before weights, or didn’t exercise at all. They trained three times a week for eight weeks. Their cardio workouts were made up of running at 70–80% of maximal heart rate for ten minutes and their weight training consisted of three sets of eight repetitions at 80% of one repetition max. The lifts they performed were leg extension, lying leg curl, tricep pushdown, bench press, and lateral pull down. Whether they did the cardio or weights first, all the workouts were separated by five minutes of recovery.

The results showed that for testosterone, there were no significant differences. For cortisol, they found significant increases in both of the training groups. There were significant decreases in the leptin and testosterone to cortisol ratio (which indicates a positive fitness response) and both training groups also had a significant loss of body fat. The interesting thing (and the take-home message) was that the “weights before cardio” group were slightly better off in every single test, including fat loss.